<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    #box{
        width: 200px;
        height: 200px;
        border: 2px solid #111;
    }
</style>
<body>
    <h1>变小狗</h1>
    <button onclick="kkk()">变宽</button>
    <button onclick="ggg()">变高</button>
    <button onclick="sss()">变色</button>
    <div id="box">
        
    </div>
</body>
<script>
    var box=document.getElementById('box')
    function kkk(){
        box.style.width='500px'
    }
    function ggg(){
        box.style.height='500px'
    }
    function sss(){
        box.style.backgroundColor='red'
    }
</script>
</html>